1 hernial Hysteresis of Fused Silica. 721 



above method oE reduction o£ Dorsey's results, their agree- 

 ment with Scheel's corresponding values for his Zeiss 

 specimen must be regarded as very satisfactory. A mean 

 of Scheel's Zeiss values and Dorsey's reduced values for low 

 temperatures is probably not far from the truth. 



High Temperatures. 



Le Chatelier * in 1900 was the first to make systematic 

 measurements on the expansion of fused silica at high tem- 

 peratures. Subsequent work has not confirmed his results, 

 which depend on the expansion of porcelain. When plotted, 

 his readings indicate a maximum length at 750° and a mean 

 expansion coefficient of *67 x 10~ 6 for the range to 1000° C. 



Gallendar f in 1901 obtained the value '59 X 10 -6 for the 

 mean coefficient of expansion between room temperature and 

 1000° C. of a silica rod 40 cms. long. He states that the 

 expansion is uniform up to 1000° C, increases rapidly 

 from 1000° to 1400°, and changes to a contraction beyond 

 1400° %. The length was measured by a micrometer 

 microscope, and the temperature was estimated by the ex- 

 pansion of a surrounding platinum cylinder which was used 

 to heat the silica. Oallendar's result reduced to the interval 

 0° to 1000° is noted in Table III. 



Holborn and Henning § in 1903 used a rod of silica 52 cms. 

 long, and by a microscope method measured the length at 

 room temperature, 250°, 500°, 750°, and 1000°. The rod 

 was heated electrically in a porcelain tube, and the tempera- 

 tures at different points of the rod were measured by a 

 thermocouple. The results have been reduced and brought 

 into line with those of observers in Table III. 



Minchin || in 1907 found "45 x 10 -6 as the uniform co- 

 efficient of expansion between room temperature and 950°. 

 Certain errors have, however, since been found in his work. 



Randall % has recently completed a comprehensive series 

 of measurements using Minchin's specimen of silica. He 

 employed an interference method over the range 16° to 

 1100°. The silica (a ring about 10 mm. long made by Zeiss) 

 was heated in vacuo by an electric furnace ; temperatures 

 w r ere taken by a Pt-Rh thermocouple. The experiments 



* Le Chatelier, Compt. Bend. cxxx. p. 1703 (1900). 

 t Callendar, Chein. News, lxxxiii. p. 151 (1901). 



I Shenstone, 'Nature,' lxiv. p. 65 (1901), gives this temperature as 

 1200°. 



§ Holborn and Henning, Ann. der Phys. x. p. 447 (1903). 

 || Minchin, Phys. Rev. xxiv. p. 1 (1907). 

 51 Randall, Phys. Rev. xxx. p. 216 (1908). 



Phil. Mag. S. 6. Vol. 20. No. 118. Oct. 1910. 3 B 



